Traditionally, thin films of Zirconium Oxide (ZrO2) have been used as high-k materials for insulating layers in capacitor structures. Recently, Niobium Oxide (Nb2O5) thin films sandwiched between two ZrO2 dielectric layers have been found to help significantly reduce leakage current and stabilize the cubic/tetragonal phase of the ZrO2. The resulting ZrO2/Nb2O5/ZrO2 stack provides higher k values in the current Metal-Insulator-Metal (MIM) capacitor of Dynamic Random Access Memory (DRAM). (Alumina, J. Vac. Sci. Techno A 4 (6), 1986 and Microelectronic Engineering 88 (2009)1789-1795).
Metal Nitride films, such as Niobium Nitride (NbNx wherein x is approximately 1) have been used for some niche applications, such as photodetectors at extremely low T (4K) where they become superconductors. Romestain et al., New Journal of Physics, Vol. 6, 2004. During the past decade, metal nitrides such as TiN, TaN, WN or NbN have increasingly been used as diffusion barrier and adhesion/glue layers in microelectronic devices [Applied Surface Science 120 (1997) 199-212]. NbCl5 for instance has been examined as a niobium source for Atomic Layer Epitaxial growth of NbNx, but the process required Zn as a reducing agent [Applied Surface Science 82/83 (1994) 468-474], NbNx films were also deposited by atomic layer deposition using NbCl5 and NH3, [Thin Solid Films 491 (2005) 235-241]. The chlorine content showed strong temperature dependence: the film deposited at 500° C. was almost chlorine free while the chlorine content was 8 at. % when the deposition temperature was as low as 250° C. Id. The 500° C. chlorine free deposition temperature may be too high for production of some semiconductor devices. The high melting point of NbCl5 also makes this precursor difficult to use in the vapor deposition process.
Gust et al. disclose the synthesis, structure, and properties of niobium and tantalum imido complexes bearing pyrazolato ligands and their potential use for the growth of tantalum nitride films by CVD. Polyhedron 20 (2001) 805-813. However, one of ordinary skill in the art will recognize that not ail CVD precursors may be suitable for ALD processes. See, e.g., Gordon et al. at https://www.scribd.com/document/310950017/ALD-an-Enabler-for-Nanoscience-and-Nanotechnology-Gordon-Harvard-Revied-Amide-Compounds.
A need remains for developing novel, liquid or low melting point (<50° C), highly thermally stable, Niobium-containing precursor molecules suitable for Atomic Layer Deposition of Nb containing films, whether insulating or conductive.